Physical sensors are widely used in many products, such as modern machines, to measure and monitor physical phenomena, such as temperature, speed, and airborne emissions from motor vehicles. Physical sensors often take direct measurements of the physical phenomena and convert these measurements into measurement data to be further processed by control systems. Although physical sensors take direct measurements of the physical phenomena, physical sensors and associated hardware are often costly and, sometimes, unreliable. Further, when control systems rely on physical sensors to operate properly, a failure of a physical sensor may render such control systems inoperable. For example, the failure of an intake manifold pressure sensor in an engine may result in shutdown of the engine entirely even if the engine itself is still operable.
Conventional data acquisition systems capture sensed values on either time intervals (at a certain frequency) or when manually triggered (as by a key phasor signal on a rotating shaft). Models of airborne emissions from internal combustion engines are generally fitted to data in the time domain at fixed intervals. However, because the engine could be operating at different speeds at different points in time, the amount of airborne emissions is not constant with respect to time. Further, because of nonlinear effects in the system from components like turbochargers, intercoolers, and the like, the rotational domain is not appropriate either. A virtual sensor network using models of airborne emissions from internal combustion engines in the time domain are often nonlinear in nature, and difficult to compute.
Instead of modeling in the time domain or frequency domain, it may be possible to transform the data into a pulse domain. In vibration theory, some analysis may be changed from a time domain approach to a shaft speed approach for certain types of modeling, pattern recognition, and virtual sensing. For example, U.S. Patent Publication No. 2004/0236494 (the '494 publication) to DeBotton et al., published on Nov. 25, 2004, discloses a method and system for diagnosing the health-condition of engines. The '494 publication uses the harmonic terms of the Fourier series representation of the engine vibration and correlates them with the mechanical state of the engine. When one of the cylinders is malfunctioning in some way, it generates a disturbance in the original ideal vibration waveform of the engine. The disturbance may appear as an increase or a decrease in the magnitude of the oscillation associated with the combustion process in the cylinder, as a variation of the waveform contour or profile, or usually as a combination of both. A malfunctioning cylinder may be detected by monitoring the magnitude and waveform contour or profile of the harmonic terms of the Fourier series representation of the engine vibration while correlating them with the mechanical state of the engine.
Although the method and system of the '494 publication may be useful for diagnosing the health-condition of engine systems and may detect malfunctioning cylinders, it still has several shortcomings. For example, the method and system of the '494 publication are useful for detection of engine state of health, but are not disclosed as useful for modeling of airborne emissions from internal combustion engines. Additionally, the method and system of the '494 publication are designed to monitor the vibration response in the frequency domain rather than to monitor airborne emissions in the combustion pulse domain. The method and system of the '494 publication do not disclose offsetting measurements for the varying shift in time for exhaust products to exit the exhaust system. A further drawback of the method and apparatus of the '494 publication is an inability to transform the modeling results back into the time domain for further use by an Electronic Control Module (ECM) or other systems or models. Additionally, the method and apparatus of the '494 publication may not allow further use of the modeling results in the combustion pulse domain by an ECM or other systems or models.
The disclosed system and method are directed to improvements in the existing technology.